Over 80% of phenols are represented by flavonols (catechins).
In black teas the processing modifies the qualitative and quantitative composition of the phenols, oxidising them enzymatically into theaflavin and thearubigin, which give the beverage its characteristic aroma and amber colour.
The teas with the highest phenol content are green, white and semi-fermented teas.
The most important of the catechins of tea is EGCG, epigallocatechin gallate.
In addition to giving the tea infusion its typical astringent flavour, the catechins also have the following properties:
• they are antioxidants
• they lower the level of LDL cholesterol (bad cholesterol) and triglycerides (fats in the blood), thus reducing the risk of cardiovascular disease
• they have a preventive effect on certain tumours
• they appear to have an inhibiting effect in relation to nicotine and reduce addiction
• they reduce glucose in the intestine and inhibit alpha amylase which is responsible for raising the glucose level in the blood after meals
• they reduce blood pressure: those suffering from high blood pressure are advised to preferably drink green tea with a low caffeine content (since caffeine has a hypertensive effect)
• they have an antimicrobial effect on streptococcus, which is responsible for dental caries: studies show that this effect is more potent in semi-fermented teas
• they have a calming effect on the mucous of the stomach and the intestine, and an anti-bacterial effect on the bacteria responsible for diarrhoea.